Isolation and molecular identification of Aeromonas species from the tank water of ornamental fishes.

Aeromonads are recognised as important pathogens of fishes. In this study, ten water samples were randomly collected from pet shops' fish tanks and home aquaria inhabited by several fish species (silver arowana, koi, goldfish, catfish, pictus fish, silver shark and silver dollar fish). Altogether 298 colonies were isolated using Aeromonas selective agar. A total of 154 isolates were then confirmed as belonging to the genus Aeromonas using the GCAT gene. Using ERIC-PCR, a total of 40 duplicate isolates were excluded from the study and 114 isolates were subjected to PCR-RFLP targeting the RNA polymerase sigma factor (rpoD) gene using lab-on-chip. A total of 13 different Aeromonas species were identified. The most prevalent species were A. veronii (27%, 31/114), followed by A. dhakensis (17%, 19/114), A. finlandiensis (9%, 10/114), A. caviae (8%, 9/114), A. hydrophila (4%, 4/114), A. jandaei (4%, 4/114), A. rivuli (3%, 3/114), A. enteropelogens (2%, 2/114), A. tecta (2%, 2/114), A. allosaccharophila (1%, 1/114), A. eucrenophila (1%, 1/114), A. media (1%, 1/114) and A. diversa (1%, 1/114). Twenty-six isolates (23%) were unidentifiable at species level. The present study demonstrates that Aeromonas species are highly diverse in freshwater fish tanks, and suggests the potential risks posed by the isolated bacteria to the health of ornamental fish species.